Among the various video display systems available in the art, an optical projection system is known to be capable of providing a high quality display in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors, wherein each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of, e.g., an optical baffle. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIGS. 1 and 2A to 2F, there are shown a cross sectional view of an array 10 of M.times.N thin film actuated mirrors 11, wherein M and N are integers, comprising an active matrix 12, an array 13 of M.times.N thin film actuating structures 14, an array 15 of M.times.N supporting members 16 and an array 17 of M.times.N mirrors 18, and schematic cross sectional views setting forth the manufacturing steps therefor, respectively, disclosed in a commonly owned application, U.S. Ser. No. 08/331,399, entitled "THIN FILM ACTUATED MIRROR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF".
The process for manufacturing the array 10 of M.times.N thin film actuated mirrors 11 begins with the preparation of the active matrix 12, having a top and a bottom surfaces 75, 76, comprising a substrate 59, an array of M.times.N transistors (not shown) and an array 60 of M.times.N connecting terminals 61, as illustrated in FIG. 2A.
In the subsequent step, there is formed on the top surface 75 of the active matrix 12 a supporting layer 80, including an array 81 of M.times.N pedestals 82 corresponding to the array 15 of M.times.N supporting members 16 and a sacrificial area 83, wherein the supporting layer 80 is formed by: depositing a sacrificial layer (not shown) on the entirety of the top surface 75 of the active matrix 12; forming an array of M.times.N empty slots (not shown), to thereby generated the sacrificial area 83, each of the empty slots being located around each of the M.times.N connecting terminals 61; and providing a pedestal 82 in each of the empty slots, as shown in FIG. 2B. The sacrificial layer is formed by using a sputtering method, the array of empty slots, using an etching method, and the pedestals, using a sputtering or a chemical vapor deposition (CVD) method, followed by an etching method. The sacrificial area 83 of the supporting layer 80 is then treated so as to be removable later using an etching method or the application of chemicals.
A conduit 73 is formed in each of the pedestals 82 by first creating a hole extending from top thereof to top of the corresponding connecting terminals 61 using an etching method, followed by filling therein with an electrically conducting material, as depicted in FIG. 2C.
In the subsequent step, as depicted in FIG. 2D, a first thin film electrode layer 84, made of an electrically conducting material, e.g., Au, is deposited on the supporting layer 80. Thereafter, a thin film electrodisplacive layer 85, made of an electrodisplacive material, e.g., PZT, and a second thin film electrode layer 95 are then respectively formed on the first thin film electrode layer 84. Each of the conduits 73 is used for electrically connecting each of the connecting terminals 61 with the first electrode layer 84 in each of the thin film actuated mirrors 11. The structure shown in FIG. 2D is, then, heat treated to allow a phase transition to take place in the thin film electrodisplacive layer 85.
Subsequently, a thin film layer 99, made of a light reflecting material, e.g., Al, is provided on top of the second electrode layer 95.
The thin film layers of the electrically conducting, the electrodisplacive, and the light reflecting materials may be deposited and patterned with the known thin film techniques, such as sputtering, sol-gel, evaporation, etching and micro-machining, as shown in FIG. 2E.
The sacrificial area 83 of the supporting layer 80 is then removed or dissolved by the application of chemical to thereby form said array 10 of M.times.N thin film actuated mirrors 11, as illustrated in FIG. 2F.
In the above described methods for manufacturing the array 10 of M.times.N thin film actuated mirrors 11, an additional process for forming an elastic layer can be added, involving a similar process as in the forming of other thin film layers.
There are a number of problems associated with the above-described method for forming the array 10 of M.times.N thin film actuated mirrors. The first and foremost to be mentioned is a build up of stress in the thin film electrodisplacive layer during the heat treatment as a result of each of the thin film layers in the thin film actuating structures 14 having a different thermal expansion coefficient. The build up of stress will cause defects, e.g., cracks or hillocks, to be formed on the thin film electrodisplacive layer 85 in each of the thin film actuated mirrors 11, which will in turn, affect the performance thereof, and, hence, the performance of the array 10.
Furthermore, the chemical or the etchant used in the removal of the sacrificial area 83 of the supporting layer 80 in each of the actuated mirrors 11 might chemically attack other thin film layers, degrading the structural integrety of each of the thin film actuated mirrors 11 which will, in turn, affect the performance thereof, and hence, the performance of the array 10.